The lead cast member of the television series, Adrian Paul, explained, "The Quickening is the receiving of all the power and knowledge another immortal has obtained throughout his/her life. It is like the receiving of a sacrament or a massive orgasm."[2] The series producers stated, "The power of the Quickening is the equivalent to a major electrical storm hitting—windows explode, lights short circuit, it is almost as if the victorious Immortal is in the center of a lightning storm."[3]

In the Highlander universe, the energy released by a Quickening is absorbed by the Immortal responsible for the beheading. The series producers explained that if "an Immortal is decapitated by something other than the sword of the Immortal he was fighting, (...) what we thought was, as long as an Immortal is present, he gets the Quickening."[4]
If an Immortal is beheaded and there is no Immortal nearby to receive the Quickening (if, for example, the beheader is a mortal), then the Quickening dissipates without effect.[citation needed]. The series producers have also revealed that, "if there is no Immortal present, then the Quickening just goes to the Source,"[4] but it is not known yet what the "Source" exactly is.

On rare occasions, the Quickening overwhelms the personality of the Immortal, even turning a good Immortal evil. This occurrence is known as a Dark Quickening in the series version.[5] The converse can also happen; Darius is the only known example of a Light Quickening.[6]

The Immortal characters are able to sense a nearby Quickening, as well as an ability to know which Immortal has been killed. Such abilities are demonstrated in Highlander: The Series, when Duncan MacLeod falls on his knees following the beheading of his friend, Lucas Desiree. Desiree is beheaded by Howard Crowley, and MacLeod knows that his friend has died.[7]

In the original Highlander film, When an Immortal beheads another Immortal, the survivor is overwhelmed by an invisible force embodied in a bright flashing light, at which point the dead Immortal's body levitates, releasing an energy charge in the surrounding area.

The Quickenings of this film do not match the other stories. One Quickening de-ages Connor, who had grown old after winning the Prize. The next Quickening resurrects Ramirez after being dead for 500 years — although it is implied that this is due to a "magical bond" between them that even death could not sever. Another odd use of the Quickening has Ramirez expelling his own life-force to stop a large machine from killing Connor. Most unusual, perhaps, is Connor's use of the final Quickening (from General Katana) to destroy the shield surrounding the Earth.

In this film, the Quickening is shown to more directly transfer knowledge and skill (as opposed to the vague transfer seen elsewhere). The plot of the movie is that the villain had beheaded an Immortal wizard and absorbed his magical abilities. In theory, Connor received these abilities at the end. Though other Highlander stories have featured Immortals with unusual gifts, none have shown the direct transfer of those gifts upon beheading. In the second Quickening, Kane beheads one of his henchmen, causing an electrical storm powerful enough to be felt by Connor MacLeod halfway around the world. This would serve to warn Connor that The Game was not over yet; whether this was an isolated event or something that happens after a long time has passed by with a temporary 'suspension' of The Game remains to be seen.

This film's Quickening sequences have a common theme, starting with Kane receiving the Immortal sorcerer Nakano's Quickening after beheading him, down to the scene where Connor receives Kane's Quickening. The transfer of energy begins with the deceased Immortal's headless body levitating and the surrounding area filling with visible electromagnetic energy capable of causing structural damage to nearby objects. The final Quickening was powerful enough to levitate Connor while he was receiving it; reminiscent of the final Quickening in the first film.

This movie represents the only two occasions of a single Immortal receiving multiple Quickenings at a time. The first occurs when Jacob Kell penetrates the Sanctuary and decapitates all of the Immortals there with the sole exception of Connor MacLeod. They were escaping The Game. Kell's "associates," who are also Immortal, may have been around to share the Quickenings. When Kell beheaded his gang in a "Last Supper"-style execution, the resulting Quickenings were powerful enough to levitate him. The final Quickening, on the other hand, was unique: a disembodied head is generated from the spot where Kell's decapitated body fell; this head shoots lightning bolts at Duncan MacLeod. Also seen during this Quickening is a spiraling plume of water and electrical discharge rising rapidly towards the clouds and generating an electrical storm that lasts until Duncan fully receives it.

The fourth Highlander movie follows the television show rather than the earlier movies; therefore, its Quickenings follow the rules of the show. Kell has amassed more than 600 Quickenings and this is reflected in his increased skill as a fighter; Connor also asserts that he must be killed by Duncan so that Duncan is strong enough to defeat Kell.

Duncan appears to briefly take on the voice and appearance of Connor at one point prior to Kell's defeat. This has only been seen on one other occasion, in "Haunted", the 7th Episode of the 5th season of the Highlander television series; it is the episode in which Jennifer Hill first meets Richie Ryan. Ryan briefly takes on the voice and appearance of Alec Hill, Jennifer's Immortal husband, whom Richie had defeated and killed the previous summer.

Criticism of the holy-ground beheadings resulted in the removal, from the DVD edition, of all references describing the Sanctuary as "holy ground."

Only two Quickenings are featured in this sequel; both are received by the Guardian. In keeping with previous Quickenings, the beheaded Immortal's essence (represented by electrical discharges) first emanates from the base of the severed neck, followed by explosions. Due to the power of the Source's manifestation, Immortals who seek the location of the Source lose their Immortality (and theoretically their Quickening). Immortal characters could thus be killed permanently without beheading, and when decapitated do not release the Quickening.

The Quickenings feature several notable differences, unique to the movie and important in both plot and character development. The first Quickening is received by the Guardian shortly after being awakened and demonstrtes two unusual effects: it magically removes a piece of armor protecting the Guardian's neck from beheading, which was attempted by the Immortal Zai several times during his losing battle with the Guardian. It also grants him the ability to use a sword drawn from his own flesh (the Guardian did not have a sword when awakened; he killed Zai with his own blade). This effectively enables the Guardian to once again participate in the Game after several thousand years of inactivity. The second Quickening is shown in a flashback several thousand years earlier in the movie's timeline. It results in a curse affecting the two Immortals surviving the battle against the previous Guardian: one was transformed into a mass of decaying Immortal flesh; the other was cursed to take the Guardian's place.

In the movie's plot, access to the Source is contingent in one of two outcomes of a contest between the Guardian and another Immortal. If the Guardian is successfully challenged and defeated by another Immortal, the Immortal is presented with a choice whether or not to decapitate the Guardian and receive his Quickening. By choosing the former, he takes the Guardian's place; if he chooses to spare the Guardian, the curse is carried by the loser and he gains access to the Source.

Highlander: The Search For Vengeance contains two Quickenings that occur in the same manner as those in the first original Highlander movie. A Japanese woman in the fields undergoes vibrations in her head and slightly rolls her eyes as she becomes immortal. Colin MacLeod's Quickening by lightning takes place inside an old Stonehenge-like structure and is very similar to Connor MacLeod's Quickening in the Highlands of Scotland.

All Quickenings featured on the television series (as well as the spin-off movie Highlander: Endgame) take the form of lightning storms striking the victor. The exact nature of each Quickening varies. With the exception of Slan Quince's Quickening in "The Gathering," the Quickening sequences begins with a foggy or misty veil enveloping the loser's fallen body; lightning storms of varying intensity then follow. Sometimes it is seen as a transfer of knowledge (represented through visions of the deceased Immortal's life or briefly taking on their mannerisms), while other times the world around the Immortal changes through cloud coverage and the passage of several hours (generally day to night). All Quickenings feature lightning and explosions (the power of the surrounding explosions also varies). Sometimes physical manifestations (ghosts, spirits) and levitation (of the receiver or nearby objects) accompanies the Quickening, especially very powerful ones.

A build up of Quickenings from evil Immortals can overwhelm even the best of Immortals and lead to a Dark Quickening. The Dark Quickening draws out the darker elements of an Immortal's psyche until they become evil themselves.

In season four episode 13 of Highlander, an Immortal Native American named Coltec, who took it upon himself to rid the world of evil by killing as many evil Immortals as he could, was eventually overwhelmed by the Dark Quickening. Duncan MacLeod was forced to kill his friend and was himself overwhelmed. Duncan then went on a rampage in Paris, ending with the beheading of another old friend, Sean Burns. Burns was known as one of the wisest and most peaceful of the Immortals and his Quickening subdued the Dark Quickening long enough for Methos to take Duncan to a long forgotten healing spring where Duncan was able to vanquish his darkness.

In the first season of Highlander, the Immortal monk Darius was introduced as an ancient warlord who led an army across Europe. When he reached the gates of Paris, Darius encountered an Immortal holy man who tried to protect the city. When Darius beheaded the holy man, his purer essence overwhelmed Darius and caused him to disband his army and spend the next thousand years living in peace on holy ground.

From the 5th season episode "Revelation 6:8," the only example of a double Quickening came as Duncan and Methos battled the remaining Horsemen in their French lair. Duncan battled the Horsemen leader Kronos, while Methos (a Horseman himself) turned against his former "brothers" and battled Silas. As Duncan and Methos won their respective battles at the same time, the Quickenings merged and split between the two of them in an unusual display of a spiraled lightning effect.

Renegade Watcher James Horton and his band of allies beheaded several immortals between 1990-1993. Since they were mortal, the Quickening was presumably lost (whether it manifested at all is uncertain). This type of beheading was featured in more detail on the spin-off series Highlander: The Raven. In one episode, the mortal character Nick beheads an Immortal by firing his gun at a huge pane of glass that then beheads the villain. With no other Immortal present, the Quickening appears as a stream of lightning floating up towards the sky. It is unknown whether this is the same effect that happened with Horton's beheadings since it was revealed later that Nick was a pre-Immortal (one who had not had his first death yet). The only time we see Horton behead an Immortal onscreen, a second Immortal is present and, though he did not deliver the killing blow, the Quickening went to him. This was also shown on Highlander: The Raven when Nick beheaded an Immortal and Amanda Darieux was nearby to receive the Quickening.

In Highlander 3: The Final Dimension, the Immortal Pierre, who says he's "tired of this immortal life", is voluntarily beheaded by guillotine. Connor MacLeod is present, but presumably out of range, and no Quickening effects are seen or heard. However, it should be noted that the flashback ends quickly after the beheading; thus, it is possible that MacLeod could have received his Quickening off-screen.

The question of how near an Immortal must be to receive a "free" Quickening may be indicated by the season 2 episode "Counterfeit." Charles Browning shoots one of the sheriff's men who is about to behead Duncan MacLeod, but later tries to kill Duncan, saying his Quickening would have been wasted if he had not intervened. Since MacLeod had not sensed Browning, the range of the "Buzz" may delineate the range of the Quickening.

In Highlander: The Search for Vengeance, a dying Dahlia kills Marcus's immortal lover by sticking a grenade in her mouth. The result is a massive spherical explosion of Quickening rather than either of the above effects.

The rules of the Highlander universe state that Immortal combat is strictly forbidden on Holy Ground, though in Endgame Jacob Kell beheaded multiple Immortals on holy ground without repercussions. In Highlander II: The Quickening, General Katana (Michael Ironside) states that the "Golden Rule" is that immortals must not fight on Holy Ground. This would explain Jacob Kell's actions in Highlander: Endgame when he beheads several Immortals at The Sanctuary, a location that Immortal Methos referred to as Holy Ground. The Immortals at the Sanctuary are all in metal restraints meaning that Immortal combat did not take place per se. The idea that they were killed on Holy Ground, however, was still controversial enough with fans that subsequent releases of the film removed any reference to The Sanctuary as Holy Ground.

In the theatrical trailer of Highlander: Endgame, Kell states that he does not care about The Game. However, when confronted by Connor MacLeod in a cemetery, Kell decides to step into the road running alongside it before fighting him. Connor at any rate, holds his sword to Kell's neck but stops short of beheading him.

At least a hint of those unknown consequences can be glimpsed in Highlander 3: The Final Dimension when, despite the rules, Kane fights Connor at a sanctuary. A foreboding atmospheric effect begins with a closeup on a statuette of The Buddha (the location on which they are fighting is a former Buddhist shrine). The fight culminates with the destruction of Connor's sword which shatters into thousands of fragments. The two immortals wisely choose to postpone their battle.

In the Season 1 episode of Highlander: The Series called "The Hunters," Darius is killed in his church. However, his beheading was carried out by mortal Watchers with no Immortal present. Therefore the rules of Immortal combat do not apply, and the Quickening may not have manifested itself.

According to Joe Dawson a Watcher legend describes "two Immortals going at it in a Temple of Apollo" in A.D. 79 in Pompeii, which may have led to the eruption of Vesuvius. However, he admits that this is only a rumor.

Immortals may be forbidden from any type of combat on holy ground; in Season 2 episode "Unholy Alliance, Part 1," Horton meets MacLeod on holy ground and claims holy-ground protection when he sees that MacLeod wants to attack him. Although MacLeod disarms Horton in the graveyard in Season 2 episode "Counterfeit, Part 2," he waits until Horton has run out the gate before he confronts him. However, in Season 1's first episode, "The Hunters," after MacLeod discovers Darius's body in his church, he mentions that Darius "must have put up one hell of a fight."

The animated series added a new type of Quickening. Because it was aimed at young children and most of the Immortals passed on their power willingly, beheadings took place offscreen and only by Kortan. The series revealed that Quickenings could occur when the donor and the recipient together gripped a sword. This is how Quentin received a Quickening.

If in the future, this becomes canon, it will mean that an immortal can give up his/her own Quickening to another at will, in addition to beheadings. In one episode, Kortan was shown killing Connor MacLeod off-screen because he refused to transfer his Quickening through the sword. Kortan later threatened Quentin with the ominous assertion, "Your head will roll at my feet as did the head of Connor MacLeod."

As the animated series was not considered to be in continuity with either the film series (up until Highlander 3) or the live action series (including the Highlander: Endgame film as it incorporated the TV series continuity fairly implicitly), Connor's death at Kortan's hand, if it was ever canon, has since been retconned out of history, due to Duncan beheading him in Endgame. For that matter, this type of Quickening was essentially ignored thereafter, including the flash episodes featuring Methos. In addition, the animated series has no direct impact on the Quickenings seen in Highlander: The Search For Vengeance, which also seemed to follow the rules of the original series.

No official explanation as given as to how this type of Quickening developed, or if it had always been possible.

In Highlander: The Series, the producers were required to make the beheadings less violent, thereby adhering to television standards. William Panzer, who was Peter S. Davis's partner and a joint executive producer, explained, "In the movies, you know, we had a lot more license. But this being television in the early 1990s, we couldn't have a lot of body parts flying around. So, we tried to use something that created the idea that somebody got their head cut off, but that it was more like a jolt of light came out of the head, and the lightning flew around them. This, I suppose, was less violent than the movie version."[8] Consequently, the Quickening scene in the pilot episode, "The Gathering," is described in the script as follows:

"We will call this shot for want of a better term, the Quickening Thrust. This will be one of our signature shots of the show. Perhaps it is a strobed, slow-motion shot. Perhaps there is particular glint to the sword as it slashes towards us on a POV shot, representing the coup de grâce which is about to be delivered. In any event what we will NOT see, is a decapitation. No head leaves the body, indeed no sword strikes the neck. Instead, we cut to : The Quickening is a blinding flash of blue light emanating from what was the bad guy and filling the screen and arcing into anything electrical nearby. Thus, street lamps, car headlights, windows, etc. are blown out."[9]

Panzer remarked about the Quickening in "Revenge Is Sweet," "... outside during day is not great for Quickenings. Quickenings like night, Quickenings like the special effects it gives you, Quickenings do not like blowing up flower pots. This is something we've learnt from experience here and we never did it again."[10]

Panzer says about the Quickening in "See No Evil," set inside the Orpheum Theatre in Vancouver, "Because it was (...) a real old theater, doing the Quickening in there was a little eerie because any kind of pyrotechnics were kinda to be used outside, were dangerous, [they were] fireworks. And we had to use a whole new system of pyro, to cap it safely inside, and everybody was kind of happy that we worked it out in the theater without burning it at all."[11]

Panzer thinks the most elaborate Quickening in the television series appeared in the Season 1episode "Band of Brothers:" "When the pyrotechnics went off, it was shot in slow motion, and so the actual take, the wide shot was two and a half minutes long, and I was still, it was probably the most amazing Quickening that we ever had."[12]